GT4e in particular is interesting in that it gets into roughly the performance territory of the Xbox One and thus games targeted at console minimums will generally work well on it too.
And don't get me started on external graphics - it seems cool in your head, but it's really pointless in practice vs. just having a desktop PC in the bread box. dGPUs are a significant portion of the cost and power use of a modern gaming PC so it makes little sense to slave them to some laptop that has been optimized to be portable and light vs. just having two separate PCs.
Also the Surface Pro 4 i7 w/ Iris graphics (GT3e) is awesome. Quite fast and great cooling solution. Expensive, but you really can't do much better in the form factor currently.
I disagree about the external gpu. Say I want a laptop that's light, quiet and power efficient, but I want to play games sometimes. My option is either to buy a gaming laptop, which is heavy and huge, or buy an appropriate laptop and a second desktop pc. Much easier to put a GPU in a case, and use it as a dock. You're only ever going to use a gaming gpu somewhere you can plug your laptop in anyway. Right now, I have a macbook with a quad i7 mobile and GT3e. It's great. Being able to dock it with an external GPU would be fantastic.
Now, an NUC-type mini computer with GT4e is a pretty interesting option. Basically a full windows PC with Xbox One performance (in D3D12 games). For me, it comes down to price. Which option gives me the best convenience, performance at an affordable price, considering I already have a nice laptop.